[jaffathecake]

> Perhaps the author meant that a footnotes's form, i.e. a number or symbol, doesn't provide context for the note itself.

Yes. I was referring to the uselessness of the linking text being a superscript number, which is as bad, if not worse, than "click here".

> While this claim is sound, it is irrelevant because a footnote link shouldn't need context; the sentence provides it.

It doesn't. The sentence gives you information about the general topic, but not about the content of the footnote, and if it's worth visiting. Whereas the note & details examples have a heading that describes the topic of the supplementary content.

> 1) All three options are more distracting because they occupy more space. And (ii) and (iii) add color. And I'd guess that readers are more likely to unintentionally skim

Are they too distracting or too easy to ignore? Make your mind up!

> In fact, a footnote occupies the minimum space possible.

Using smaller text is a bug, not a feature.

> 2) Option (ii) adds lots of unseemly vertical space to the webpage.

Vertical space is cheap. And in the example it's hardly lots.

> 3) Option (iii) moves the webpage text below the note up and down. This interferes more with the reading experience than does the static popover.

It only moves it down, and then you can read the content in flow.

> 4) Options (ii) and (iii) are not portable over copy paste. If you copy a webpage with these elements into another file, you'll have to manually rearrange them to appear as actual footnotes.

That's a feature, not a bug. Content is in the correct order.

> 5) All options, as implemented by the author, eliminate the key-value nature of footnotes. One cannot refer to a particular parenthetical, `note`, or `<details>` because they aren't numbered.

So? They have headings instead.